I found the message boards through Hobbyspace, but was completely unable to find a link to it on the X-Prize site. Even using the search function for "Message Board" or "Forum" fails to turn anything up.

The "unveiling" of the messageboard is underway. We've posted a link on the homepage, and will be updating the rest of the site navigation over the next week. Thanks for joining, and being a part of our "community building stage"!